This invention relates to a lubricant filter for internal combustion engines, particularly of motor vehicles, provided with a reservoir of additives.
More particularly, the invention relates to a filter of the screwed-on type, in which the additives of the reservoir can be introduced into the flow of the lubricant when desired.
Some types of lubricant filters for internal combustion engines are known which contain mixtures of additives designed to integrate or replace the additives that are originally present in the lubricant and after a certain period of operation are normally exhausted or degraded.
The prevalent conception of these filters with regard to the introduction of additives is such as to provide a gradual and prolonged introduction of the additives into the flow of lubricant. This is achieved, for example, by impregnating or coating the filtering material with slowly soluble additives (U.S. Pat. No. 2,310,305; or by stocking the additives in a container having permeable walls exposed to the flow of the lubricant (U.S. Pat. No. 3,749,247); or by providing a solid mix of additives accommodated in the filter in direct contact with the flow of lubricant (U.S. Pat. No. 4,075,097).
A filter designed by the Applicant himself and described in U.S. Pat. No. 4,265,748 on the other hand, is based on a different principle of introduction of additives, namely on the complete and sudden introduction of the additives into the flow of the lubricant only after a certain period of operation when the original additives are supposed to be completely exhausted or degraded. This is obtained by placing the additives in a container inside the filter, provided with at least one wall that is slowly soluble in the lubricant so as to produce, when the wall has been completely dissolved, the complete and immediate introduction of the additives into the lubricant. The moment of introduction is determined in advance as a function of the life of the lubricant on the basis of the chemical nature and the physical structure of the soluble wall of the container.
Filters of this type with slow introduction of additives into the lubricant are not considered satisfactory for optimum duration and quality of modern lubricants as these lubricants, when they are brought into commerce, already contain additives in such an amount as to ensure a good performance over a long period of time so that it is neither necessary nor correct to increase the level of additives from the very beginning even if only in a gradual manner.
On the other hand, the filter disclosed in the U.S. Pat. No. 4,265,748 mentioned above, although it is based on a more correct principle of introduction of additives, does not permit to determine exactly the moment of introduction of the additives into the flow of lubricant as this moment, in addition to the characteristics of the soluble wall of the container, also depends on the operating conditions, on the state of the engine and on other factors which cannot be exactly ascertained or determined in advance.
It is an object of the present invention to eliminate or reduce the disadvantages of the above-mentioned filters by providing a lubricant filter for internal combustion engines, particularly of motor vehicles, which permits to introduce additives into the flow of lubricant in the moment desired by the user, independently of the mileage covered and of the chemical and physical characteristics of the additives and their container.